Steering of full-track vehicles is controlled by varying the speed or stopping the motors of drive to each track usually by separate manual controls.
For example, foot operated pedals, one to control the left track and the other to control the right track have been used. Such an arrangement requires a careful coordination of pedal displacements to maintain a straight course of constant turning rate. The use of both pedals is required for straight ahead, reverse and spin-turn operations.
Accordingly, the present invention is directed to obviating the problems with such an arrangement.
In accordance with the present invention, the hydraulic steering control circuit utilizes pilot pressures, produced by a manual displacement of a remote hydraulic controller, to produce proportional displacements of conventional directional valves, and therefore proportional control of hydraulic motors and, in turn, track speeds.
In the preferred form, the present invention utilizes a remote hydraulic controller of a type commercially available from several manufacturers world-wide which includes a manually operated lever known as a "joystick". Manual displacement of the "joystick" lever produces an output pressure proportional to lever displacement angle from the vertical at any one of four pilot pressure output ports, with the pressurized port location corresponding to the direction of lever motion. If the lever is moved in a direction between two output ports; instead of directly toward one, both ports will develop pressure, and the ratio of the two pressures will be a function of the directional angle.
The hydraulic circuit senses the higher of the two signals and this higher signal is utilized to actuate the hydraulic motor which drives the appropriate track.
The hydraulic steering system embodying the invention is designed to meet the following requirements:
1. A single control for one-handed operation.
2. Capability of driving forward or reverse, straight, or in steering turns.
3. Pivoting turns with one track locked, and the other driving, either forward or in reverse.
4. Pivoting with one track driving forward, and the other in reverse.
5. Direction of vehicle motion to correspond with direction of controller lever motion.
6. Track speed proportional to controller lever displacement.